1. Field of the Invention
This invention relates to a method for the determination of the resistivity of an n-type silicon wafer. More particularly, this invention relates to a method for the determination of the true resistivity of an n-type silicon epitaxial layer by the four point probe method.
2. Description of the Prior Art
As a way of determining the resistivity of a silicon epitaxial layer grown on a silicon substrate, the four point probe method illustrated in FIG. 10 has found wide spread acceptance.
This method determines the resistivity of a sample S by arranging four point probes 1 to 4 equidistantly on the surface of the sample S, forming a flow of a direct current I from the two outer probes to the sample S, and measuring the voltage V which occurs consequently between the two inner probes. In FIG. 10, N stands for an n-type region, P for a p-type region, t for the film thickness of an epitaxial layer, and 5 for a p-n junction.
By this method of determination, the resistivity p of the epitaxial layer can be obtained in accordance with the following formula (1): EQU .rho.=aRt (1)
wherein a stands for the constant (.pi./1n2), R for the sheet resistance of the epitaxial layer, and t for the film thickness of the epitaxial layer.
In the case of the n-type epitaxial layer, the sheet resistance R is determined by obtaining growth of this n-type epitaxial layer on a p-type silicon substrate and actually measuring the sheet resistance by the four point probe method. The film thickness t of the epitaxial layer is generally determined by measuring the film thickness of an epitaxial layer which is grown on a high-concentration antimony substrate in accordance with the Fourier-Transform Infrared Spectroscopy (FTIR) method. The resistivity .rho. is the product of R multiplied by t and a, a constant.